1. Field of the Invention
The present invention relates to a variable valve mechanism for an internal combustion engine.
2. Description of Related Art
There has been known a variable valve mechanism that changes a maximum lift amount of an intake valve, which is one of engine valves, according to an engine operation state, as described in Japanese Patent Application Publication No. 2004-339951 (JP 2004-339951 A), for example. The variable valve mechanism described in JP 2004-339951 A includes: a control shaft that changes a maximum lift amount of the intake valve according to displacement in an axial direction; a cam that abuts with the control shaft and rotates the control shaft so as to displace the control shaft in the axial direction; a motor that pivots the cam, and the like. The maximum lift amount is changed by changing a rotational phase of the cam so as to change a displacement amount of the control shaft in the axial direction. In a cam surface of the cam, a change zone in which the maximum lift amount changes due to changes in the displacement amount of the control shaft, and a retention zone in which the displacement amount of the control shaft is constant and the maximum lift amount is retained at a constant value are formed. In the variable valve mechanism, the maximum lift amount is changed by changing the displacement amount of the control shaft by use of the cam surface in the change zone. Meanwhile, by retaining the displacement amount of the control shaft at a constant value by use of the cam surface in the retention zone, the maximum lift amount is retained at a constant value even when current application to the motor is stopped. Further, as such a retention zone, a plurality of retention zones in which to retain different maximum lift amounts is provided, thereby making it possible to retain the different maximum lift amounts.